ABSTRACTPerfluorooctanesulfonyl fluoride (POSF)–based materials include surfactants, paper and packaging treatments, and surface (e.g., carpet, upholstery, textile) protectants. A metabolite, perfluorooctanesulfonate (PFOS, C8F17SO3−), has been identified in the serum and liver tissue of nonoccupationally exposed adults and wildlife. Results from several repeat-dose toxicological studies consistently demonstrate that the liver is the primary target organ with an apparent threshold for the toxic effects of PFOS that can be expressed in terms of cumulative dose or body burden. The purpose of this study was to characterize the distribution of PFOS and six other fluorochemicals in 598 serum samples obtained from a multi-center study of children (ages 2–12) diagnosed with group A streptococcal infections. Using high-pressure liquid chromatography tandem mass spectrometry methods, serum PFOS concentrations ranged from 6.7 ppb (ng/mL) to 515 ppb (geometric mean 37.5 ppb, 95% CI 36.0–39.1) with an estimate of the...